Gear train for gas turbine engines

ABSTRACT

A triple lay shaft gear train for a two-shaft gas turbine engine. The gear train includes a lay shaft mounted overrunning clutch which permits a uni-directional lock-up of the power turbine and gasifier turbine when synchronous speeds have been reached and a positive lock-up coupling means which permits selective bi-directional lock-up of the lay shafts to provide the advantages of both single-shaft and two-shaft turbine operation. The gasifier turbine and power turbine are capable of different rotational speeds.

United States Patent Carter et al.

GEAR TRAIN FOR GAS TURBINE ENGINES Inventors: Carl W. Carter, Peoria;Lloyd E.

Johnson, East Peoria, both of 111.

Assignee: Caterpillar Tractor Co., Peoria, 111.

Filed: Jan. 25, 1971 Appl. No.: 109,393

US. Cl. ..60/39.l6 R Int. Cl ..F02c 3/10, F020 7/02 Field ofSearch.....60/39.l6 R; 74/331, 661, 718

References Cited UNITED STATES PATENTS Kronogard et al. ..60/39.l6 R

3,507,113 4/1970 l-lerrmann et a1 ..60/39.16 R 3,546,879 12/1970 Hass..60/39.16 R 3,626,692 12/1971 Kamm ..60/39.16 R

Primary Examiner-Charles J. Myhre Assistant Examiner-Thomas C. PerryAttorneyCharles M. Fryer et al.

[57] ABSTRACT A triple lay shaft gear train for a two-shaft gas turbineengine. The gear train includes a lay shaft mounted overrunning' clutchwhich permits a uni-directional lock-up of the power turbine andgasifier turbine when synchronous speeds have been reached and apositive lock-up coupling means which permits selective bidirectionallock-up of the lay shafts to provide the advantages of both single-shaftand two-shaft turbine operation. The gasifier turbine and power turbineare capable of different rotationalspeeds.

1 Claim, 3 Drawing Figures PATENTEUHARZYIQYS ,722,213

sum 10F 2 INVENTORS RL CARTER OY .JOHNSON BY I a hjwwqw 44w TTORNEYS:ElE l PATENTEDHARZYIQB 3 2,213

sum 20F 2 INVENTORS CARL W. CARTER LLOYD E.JOHNSON ATTORNEYS GEAR TRAINFOR GAS TURBINE ENGINES BACKGROUND OF THE INVENTION This inventionrelates to a new and improved gas turbine engine. More particularly, theinvention is directed to a gearing arrangement for a two-shaft gasturbine engine which allows enjoyment of the advantages of bothtwo-shaft and single-shaft operation.

Single-shaft gas turbine engines are desirable in applications requiringrelatively constant operating speeds. However, in these applications thesingle-shaft arrangement has the disadvantage of requiring a very highstarting torque since the starting device utilized has to turn thedriven load and accessories in addition to the gasifier turbinecomponents. Very large starter units are required with consequent lossesin efficiency, economy, and usable space.

One attempt to solve this problem has been the utilization of atwo-shaft gas turbine engine which has separately mounted gasifierturbine and power turbine units. With this type of system, the startingtorque requirement is substantially reduced because the starting unit isrequired to turn only the gasifier turbine upon start-up. A one-way oroverrunning clutch is generally provided in this arrangement tooperatively connect the load driving turbine to the gasifier turbine forunitary rotation when normal operating speed is reached. Such a systemis shown by US. Pat. No. 2,591,540 to Grylls. However, in situationswhere dynamic braking of the driven load is required, the overrunningclutch is inadequate. A positive lock-up-of the gasifier and powerturbines, equivalent to a singleshaft operation, is required.

Another important consideration in two-shaft gas turbine engines isspace utilization. It is extremely desirable in most installations toprovide gear trains with small radial and axial dimensions.

This invention is principally directed to a coupling means forconnecting a gasifier turbine to a power turbine in a two-shaft gasturbine engine which has very small dimensions both axially andradially.

One object of this invention is to provide a gear train for coupling theturbines in a two-shaft gas turbine engine which produces low loads onindividual gears and bearings.

Another object of this invention is to provide a coupling means which isselectively operable during turbine rotation and which provides apositive lock-up between the gasifier turbine shaft and the powerturbine shaft.

Another object of this invention is to provide a shifting mechanismwhich allows a twoshaft gas turbine engine to be started in an unloadedcondition and converted to a single-shaft operation when operatingspeeds are attained.

Yet another object of this invention is to provide a gas turbine enginegear train which distributes loading through a triple lay shaft systemto reduce individual gear sizes and gain consequent savings in space.

Another object of this invention is to mount the coupling means for thegasifier turbine and the power turbine upon relatively low speed layshafts to reduce critical balancing requirements.

Still another object of this invention is to provide a speedsynchronizing overrunning clutch to couple the relatively low speed layshafts of a two shaft gas turbine engine to avoid the high levelcentrifugal force and stress conditions associated with the high speedprincipal turbine shafts.

Other objects and advantages of the present invention will becomeapparent from the following descriptions and claims.

The accompanying drawing shows by way of illustration the preferredembodiments of the present invention and the principles thereof. It isrecognized that other embodiments of the invention utilizing the same orequivalent principles may be used and the structural changes may be madeas desired by those skilled in the art without departing from thepresent invention and the purview of the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of atwo-shaft gas turbine engine system utilizing the present invention;

FIG. 2 is a schematic isometric view of the gear train arrangement ofthe present invention;

FIG. 3 is a longitudinal sectional view of the gear train and couplingmeans of the present invention.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a schematicrepresentation of a typical two-shaft gas turbine power plant whichcould embody the principles of the present invention. As shown in FIG.I, a compressor C, which is driven by a gasifier turbine T suppliescompressed air to the combustion chamber CC in which fuel and air areburned to produce working fluid for both the turbine T and the powerturbine T which drives a load 1 through the power turbine shaft 2. Thegasifier turbine is drivingly connected to the compressor throughthegasifier turbine shaft 3. The present invention is directed to meansfor selectively connecting the shafts 2 and 3.

FIG. 2 shows a schematic representation of the gear train transmissionof the present invention. The gasifier turbine gear set is showngenerally at 12 and a power turbine gear set is shown generally at 14. Areduction gear set, shown generally at 48, connects the power turbinegear set to the load output shaft 56. Three lay shafts 50 are providedfor each of the gear sets 12 and 14. These lay shafts normally operateat speeds substantially less than the shafts 2 and 3. The coupling meansof the present invention for each of the respective lay shaft sets, andconsequently for gasifier-and power turbine shafts, would be provided ateach of the locations designated 16 in the drawing. By inserting thecoupling means between the relatively low speed lay shaft as opposed todirectly between the main shafts 2 and 3, less precise alignment andbalance tolerances are required.

FIG. 3 shows a detailed view of the coupling and gear train componentsof the present arrangement. Indicated generally at 10 is one of thethree lay shaft and coupling units which are positioned in the locations16 as shown in FIG. 2. As can be seen in the drawing, the gasifierturbine shaft 3 is in constant engagement with the gasifier turbine gearset 12..Similarly, the power turbine shaft 2 constantly engages thepower turbine gear set 14. The gear ratio in the sets 12 and 14 may bedifferent to allow the power turbine shaft and the gasifier turbineshaft to operate at different speeds. Generally the overall efficiencyof the power plant can be improved substantially if the gasifier turbineis designed to operate at higher rotational speed than the powerturbine. An overrunning or sprag clutch 18 is disposed between the gearsets 14 and 12. This clutch will permit torque transmission in only onedirection. It will jam and provide a positive connection between itsdriving and driven elements whenever the power turbine gear set 14attempts to assume a speed greater than that of the gasifier turbinegear set 12. The overrunning clutch will not be described in detailherein as it is one of several such devices manufactured for the purposeof uni-directional torque transmission.

Coupling means comprising a coupling collar 26 and a piston means 22 arealso shown. These means provide a positive lock-up between the two gearsets when desired. As more fully described hereinafter, the couplingmeans operates to positively lock-up the respective gear sets whenengaged to provide what is equivalent to single-shaft engine operation.

When the gas turbine engine is to be started, a conventional startingsystem (not shown) directly communicates with and turns the gasifierturbine gear set 12 in the convention manner. At start-up, the couplingmeans 26 is in the disengaged position shown in FIG. 3 and theoverrunning clutch 18 is unjammed so that the gasifier turbine gear setand the power turbine gear set are in the uncoupled state. As thegasifier gear set is brought up tooperating speed, the power turbinegear set begins to rotate by virtue of the impingement of working fluidupon the power turbine blades in the known manner. Then the gasifiergear set reaches approximately 65 percent of its rated speed, and ifexternal work output has yet to be demanded of the engine, the powerturbine gear set will accelerate, reach gasifier gear set speed and thenattempt to surpass it. At this point, the overrunning clutch l8 jams andcauses the power turbine to drive the gasifier turbine. The automaticoperation just described with reference to one of the coupling unitsoccurs simultaneously in all three of said coupling units.

In order to provide a selectively operative, positive lock-up in eitherdirection of shaft rotation, the coupling collar means 26 is provided tointerengage a spline 30 on the power turbine gear set and the spline 28on the gasifier turbine gear set. When this interengagement is desired,oil under pressure is directed into a chamber 20 to force a piston 22leftwardly as shown in FIG. 3 against the biasing force of a compressionspring 24. The piston 22 carries the coupling collar 26 in a groove 32which is provided with bearing means 34 which allow free rotation of thecoupling collar within said groove. The coupling collar is rotatablydisposed within the internal spline 28 of the gasifier gear set, asshown. When the piston 22 moves leftwardly, the coupling collar'splineand the power turbine gear set spline 30 come into contact. The side inrelation to an engine having a triple lay shaft trans-.

lay shaft set assemblies, only one overrunning clutch 18 would benecessary to lock he gear sets in synchronous speed. In practice, one ofthe three couplings would engage prior to the other two couplings toprovide a sequential lock-up of the two gear set systems.

Disengagement ofthe coupling means would occur whenever the oil pressurein chamber 20 was released. The ingress and egress of oil to the chamber20 can be controlled either manually or in response to any of thewell-known engine parameters such as speed, temperature or pressure inthe well-known manner. It should also be noted that either a singleannular actuator piston for all three of the coupling collars 26 couldbe used or a separate actuator for each coupling collar could beutilized.

It should be noted that although the novel coupling means of the presentinvention has been described here mission, it is apparent that saidcoupling means has utility in single lay shaft arrangements.

While the preferred embodiments of the invention have been illustratedand described, it is to be understood-that these embodiments are capableof variat ion and modification and are not limited to the precisedetails set forth, but rather include such variations and modificationsas fall within the scope of the'appended claims.

What is claimed is:

1. In a two-shaft gas turbine engine having a gasifier turbine mountedfor rotation upon a first shaft means and a power turbine mounted forrotation upon a second shaft means and having three lay shaft means foreach of said first and second shaft means; first means associated witheach of said lay shaft means for selectively coupling said first shaftmeans and said second shaft means in a positive, bidirectional lock-upduring rotation of said first and second shaft means, said first meansincluding gear means operatively associated with each of said first andsecond shaft means and a selectively actuated coupling collar meanshaving spline means which directly coact with spline means on said gearmeans, pressure-actuated piston means for positively moving saidcoupling collar spline means into engagement with said spline means onsaid gear means, and second means including an overrunning clutch forcoupling said firstshaft means and said second shaft means in responseto the achievement of synchronous speed between said first andsecond'shaft means.

1. In a two-shaft gas turbine engine having a gasifier turbine mountedfor rotation upon a first shaft means and a power turbine mounted forrotation upon a second shaft means and having three lay shaft means foreach of said first and second shaft means; first means associated witheach of said lay shaft means for selectively coupling said first shaftmeans and said second shaft means in a positive, bidirectional lock-upduring rotation of said first and second shaft means, said first meansincluding gear means operatively associated with each of said first andsecond shaft means and a selectively actuated coupling collar meanshaving spline means which directly coact with spline means on said gearmeans, pressure-actuated piston means for positively moving saidcoupling collar spline means into engagement with said spline means onsaid gear means, and second means including an overrunning clutch forcoupling said first shaft means and said second shaft means in responseto the achievement of synchronous speed between said first and secondshaft means.